This invention relates to insulating refractories and more particularly, to lightweight, porous, refractory insulating castables suitable for use in lining secondary ammonia reformers.
Most ammonia and ammonia derivatives are currently manufactured by the steam reformed process. In this process natural gas or refinery gas is cracked or broken down over a catalyst, such as nickel, by combining with steam to yield hydrogen, carbon monoxide and carbon dioxide. These gases are then passed into a secondary reformer where air is introduced and combustion occurs removing free oxygen by conversion to water with some hydrogen.
If silica is present in the refractory, it will be leached out and deposited downstream in the unit. The present compositions are characterized by having low density and are composed of low silica aluminas that previously had not been used in this manner. Use of these special aluminas in the castable results in lower density and better insulating values.
It has been well known and understood in the art that various combustibles can be mixed with unfired refractory material so that, after forming and firing, a porous skeletal structure for use as a refractory insulation, will result. The combustibles have included various organic materials both naturally occurring and synthethic. Diatomaeous earth, gas developing materials and foaming agents, fly ash, asbestos, exfoliated pyrophyllite, mica and the like have also been suggested and utilized in forming a low density, lightweight refractory insulation material.
The present refractories may be defined as those of the high alumina type and are classified according to their Al.sub.2 O.sub.3 contents into groups having, approximately, greater than 50% Al.sub.2 O.sub.3, by oxide analysis. Those containing 50 to 90% of Al.sub.2 O.sub.3 are made by blending the various high alumina refractory materials, while those of 99% content are made of high purity alumina. The more common high alumina refractory materials and their typical Al.sub.2 O.sub.3 contents are discussed and set forth in U.S. Pat. No. 3,067,050 issued Dec. 4, 1962 for "Alumina Refractories".
The present invention is predicated upon a discovery that high alumina refractory monolithic bodies having densities typical of insulating refractories, and yet having high temperature strength and wear resistance similar to much denser bodies, may be prepared from batches according to this invention.